Electronics > Projects, Designs, and Technical Stuff

Dip Switches

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bostonman:
I'm confused about something. I have a really old garage door opener (Craftsman 139.653000) and want to change the code which requires changing dip switches. The manual states (which makes sense) both the receiver and remote need to have the same dip settings.

The remote seems to have three positions (+, -, and 0) and I don't understand why. Also, the receiver has push-button dip switches and I don't know if up/down mean on or off. Can someone tell me the meaning of the three-state dip switch and also whether up is a 'on' or 'off' on the other?

On a side note, something doesn't seem correct because I changed the dip switches in the receiver only, and the remote still activates the door opener. I returned the dip switches to their original state, changed the dip switches in the transmitter, and the opener still works. So it's like the dip switches don't affect the 512 security possible combination options; although the manual states otherwise.

Here are pics of the dip switches:





tsman:
The receiver sounds faulty if the dip switches don't affect it at all as they're definitely there to set the house code.

For the transmitter: + = ON, - = OFF and 0 = unconnected.

For the receiver: Pushed in on the left = ON and pushed it on the right = OFF. It is a rocker switch so you can only push in one side.

The IC in the transmitter has a trinary code hence why it has 3 different states on the switch. It'll probably be something like the old Motorola MC14502 encoder IC. The decoder IC in the receiver they're using is binary only which is why it only has 512 different codes and only has ON/OFF on the switch.

The MC14502 encoder datasheet says:


--- Quote ---Each transmitted trinary digit is encoded into pulses. A logic zero (low) is encoded as two consecutive short pulses, a logic one (high) as two consecutive long pulses, and an open (high-impedance) as a long pulse followed by a short pulse.
--- End quote ---

Buriedcode:
That is indeed confusing - about changing the DIP switch settings and the device still working, often these things use the PT2272/PT2262 or equivalent (HT12D/E series) devices that have ten tri-state address settings.  That might explain the use of a tristate DIP switch - each of the 8 are either, VCC, GND or High-Z (not connected to either).

It seems the receiver is using a two-state DIP switch, although it is hard to tell from the photo it looks like pushing down on one end of the switch, raises the other, so its either connected, or not.  You can check this by looking on the underside to see if it has two rows or 8 pins, or three.

If you have access to the encoder chip in the transmitter, and a logic analyzer, you can see the output which is explained in the datasheet for the encoder chip (whichever one its using). But to me it certainly looks like the transmitter address is 10ZZ10ZZ1, whilst the receiver has 101101101. Odd.  It could be the receiver doesn't use a standard decoder, but a microcontroller, that can accept more than one address (a learning receiver).

bostonman:
Sorry, I should have stated that pushing down on one raises the other side (on the receiver dip switches).

Using the 'off' side of the dip switches as reference, I can't tell if when the button is down, whether that's 'off' or it needs to be up to be 'off'.

Initially I tried to figure out this by comparing the 'up' and 'down' state of each switch to the transmitter, however, when I saw the transmitter was tri-state, I got really confused because the switch states didn't match.

My focus was on dip switches 1-3. So I moved all three on the receiver only, and the transmitter still controlled the door opener. I returned the switches, and moved all three on the transmitter, and was still able to control the garage door opener.

I'll investigate it more this weekend, but I'm confused. A contractor has essentially stolen my spare remote, so I'm trying to change the code to avoid him accessing my garage.

madires:
If you like to improve security you can buy kits with key fobs and a matching receiver module supporting rolling code. The receiver module has a relay for interfacing the garage door opener. And don't forget to disable the old receiver circuitry. I've done this mod last year for two garages and it was fairly easy. IIRC, I paid 40 bucks for each kit with two fobs and a two channel receiver.

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